Dealing with Aphids in Your Greenhouse
There is nothing more vexing than discovering that aphids have begun to invade your garden greenhouse, munching away on your luscious vegetables. This is a common fall problem that has a variety of control options: prevention, minimal controls, insecticidal soaps, and biological controls.
Keep them out! - Carefully monitoring plants you bring into your greenhouse is the first step in dealing with aphids. Choose healthy and vigorous plants, and spray them down with your garden hose to knock off any hitchhikers before you bring them into your greenhouse. If the plant has an obvious insect infestation, do not bring it into your greenhouse. Period. If you must, spray it with an insect control spray, or enclose it with a plastic bag in which you place an insecticide strip for two or three days. Hose your plant down after taking it out of the treatment bag, before transplanting it to your greenhouse.
No control or minimum control - Sometimes aphids can become established no matter how careful you are in your preparations and preventative tactics. In this case, there are several alternative paths you can take. If you are a purist and do not want to use insecticides in our greenhouse environment, you have a couple options. Hosing down infected plants with a powerful stream from your garden hose can be effective for a while. If you plan on closing down your greenhouse soon, this may be the best option. Some hobby greenhouse gardeners choose to shut their greenhouse down for anywhere from 2-4 months in the winter allowing Mother Nature to take over and freeze out insect pests. If you want a little more aggressive natural control, diatomaceous earth is effective. You can sprinkle this powder on and under leaves of effected plants. If you catch the problem early and have isolated insects in one part of your greenhouse, this can be an effective control.
A more aggressive approach - Another way to control your aphid problem is to use a fast acting insecticide that is safe for using on vegetable gardens. There are several varieties out there that are “garden safe.” Check your local garden center or hardware store for alternatives. Most of these involve an organic insecticidal soap that takes care of aphids, or at least significantly reduces their number. You can also make your own version of this by mixing a tablespoon of liquid dish detergent with water in a quart sprayer. The soap coats the aphids and reduces their numbers. You have to spray every day for best results, paying particular attention to the underside of leaves of infected plants.
Another alternative to aphid control are biological controls, such as lacewings, ladybugs and midges. Several companies provide these predators for your greenhouses. If using this approach, be sure to limit your use of insecticidal spray, as it will kill off your predator population, as well as your pests.
Using a combination of the above controls, you can keep your greenhouse healthy and productive throughout the fall and winter greenhouse growing seasons.
Betsy Woodworth writes about gardening and also about garden building.
